1. Field of the Invention
The present invention relates generally to a phase noise elimination apparatus and method.
More particularly, the present invention relates to an apparatus and method for feedforward-type phase noise elimination in a portable terminal, which detect and eliminate phase-reversed phase noise by subtracting a GSM transmission signal, passed through the power amplifier of a GSM transmission device, from a GSM transmission signal, extracted from an upstream stage of the power amplifier, so that phase noise signals attributable to high-power transmission signals, such as GSM transmission signals, can be blocked at the time of receiving digital TV broadcasts, such as DVB-H broadcasts, and, as a result, the deterioration of reception sensitivity for digital TV broadcasts occurring due to the phase noise signals of high-power GSM signals can be prevented, thus improving reception performance for digital TV broadcasts, such as DVB-H broadcasts and the productivity of portable terminals.
2. Description of the Related Art
Generally, as great attention has recently been paid to digital TV broadcasting, technology for DMB in Korea and technology for DVB in European areas have been developed.
Here, the term “DMB” is an abbreviated form of “Digital Multimedia Broadcasting”, which includes terrestrial DMB and satellite DMB. Further, the term “DVB” is an abbreviated form of “Digital Video Broadcasting”, which includes DVB-T, in which a fixed device for home- or office-use receives broadcasts from a typical broadcasting station, and a DVB-H, in which the low power consumption, mobility and portability of mobile phones or portable video devices are taken into consideration.
Further, it is expected that, as portable terminals including mobile communication terminals, such as mobile phones or Personal Digital Assistants (PDAs), have composite characteristics, portable terminals equipped with DVB-H devices will be introduced. At this time, there is required a suitable countermeasure to cope with a phenomenon, in which, when two or more functions (Global System for Mobile communications [GSM]/General Packet Radio Service [GPRS] and DVB-H) are supported in a single terminal, reception sensitivity of each module is deteriorated due to interference between the two or more functions.
FIG. 1 is a diagram showing the construction of a conventional GSM portable terminal equipped with a DVB-H receiver.
Referring to FIG. 1, a conventional GSM portable terminal includes a GSM transmitter/receiver 11 for transmitting or receiving GSM signals of about a 900 MHz frequency band (TX: 880˜915 MHz and RX: 925˜960 MHz) and a DVB-H receiver 12 for receiving DVB-H broadcast signals of a frequency band ranging from about 470 MHz to 750 MHz.
The influence of phase noise of the GSM900 transmission (TX) band corresponding to about 900 MHz on a DVB-H reception (RX) band is described below with reference to FIGS. 2A and 2B.
FIGS. 2A and 2B are diagrams showing the influence of phase noise of a GSM900 TX band on a DVB-H RX band in a conventional portable terminal. FIG. 2A illustrates the influence of phase noise of a GSM900 TX band on a DVB-H RX band when a band pass filter for removing signals of the GSM900 TX band is not included in the input stage of the DVB-H receiver 12, and FIG. 2B illustrates the influence of phase noise of a GSM900 TX band on a DVB-H RX band when a band pass filter for removing signals of the GSM900 TX band is included in the input stage of the DVB-H receiver 12.
Referring to FIG. 2A, the DVB-H band is a band ranging from about 470 MHz to 750 MHz, and the GSM900 TX band is a band ranging from about 880 MHz to 915 MHz. FIG. 2A shows that the phase noise signal of a GSM TX signal flows into the DVB-H RX band, and then negatively influences a DVB-H RX signal.
Meanwhile, in a conventional portable terminal, a situation may occur in which GSM transmission/reception is performed through the GSM transmitter/receiver 11 while a digital broadcast is received through the DVB-H receiver 12. Further, a situation may also occur in which GSM transmission/reception is performed through another GSM transmitter/receiver placed close to the DVB-H receiver 12 while a digital broadcast is received through the DVB-H receiver 12.
Referring to FIG. 2B, since the GSM transmitter/receiver 11 amplifies the power of a GSM TX signal to high power of about +33 dBm through an internal power amplifier, such a high-power GSM TX signal may flow into the DVB-H receiver 12 through an antenna. In this case, the GSM TX signal acts as noise on an RX signal for a DVB-H broadcast. Therefore, in order to reduce this noise, a Band Pass Filter (BPF) may be included in the input stage of the DVB-H receiver 12. The BPF passes a DVB-H RX signal of about 470 MHz to 750 MHz therethrough and blocks a GSM TX signal of 880 MHz or more.
The BPF included in the DVB-H receiver 12 of the conventional GSM portable terminal blocks the GSM TX signal, thus removing the influence of noise attributable to intermodulation between the GSM TX signal and the DVB-H signal, which is caused in the RF circuit of the DVB-H receiver 12.
However, such a conventional GSM portable terminal is problematic in that, even if a BPF is included, a phase noise component included in a GSM TX signal of a 470 MHz to 750 MHz band corresponding to the DVB-H RX band is not blocked, but passes through the BPF without being attenuated, and influences the DVB-H RX band, thus deteriorating reception sensitivity for DVB-H broadcasts.
Such a problem of the conventional GSM portable terminal will be described in detail with reference to FIG. 3.
FIG. 3 is a graph showing the influence of phase noise-versus DVB-H reception sensitivity measured in the conventional GSM portable terminal. The graph of FIG. 3 shows the deterioration characteristics of DVB-H reception sensitivity corresponding to the phase noise level of a GSM TX signal, measured when a GSM TX signal flows into the DVB-H receiver 12 through a second antenna ANT2, and the phase noise of the GSM TX signal influences a DVB-H RX band.
Referring to FIG. 3, it can be seen that the reception sensitivity of the DVB-H receiver 12 is deteriorated by about −24 dB in such a way that, referring to reception sensitivity G11, obtained in the absence of the influence of phase noise, and G12, obtained in the presence of the influence of phase noise, reception performance is decreased from −93.5 dBm (G11) to −69.5 dBm (G12), when the phase noise level of a GSM TX signal flowing into the DVB-H receiver 12 through the second antenna ANT2 is −150 dBm/Hz.
That is, the conventional GSM portable terminal is problematic in that, since the attenuation of a GSM TX signal is not sufficiently realized by using the BPF, such a GSM TX signal flows into the DVB-H receiver 12 as a noise component, thus decreasing reception sensitivity for DVB-H broadcasts.